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# Fastener Flexibility Application for this Scenario

## Fastener Flexibility Application for this Scenario

(OP)
Folks,
Let's say I want to calculate Shear Flexibility of a fastener/rivet in a joint using equation such as Huth for FE input.

The joint shown below is hypothetical but I want to learn on how to tackle a joint made of dissimilar materials & different thicknesses.

In the above joint, the fastener is under double shear. All the 3 plates in the joints are of different thicknesses & materials.

1. If I am modeling a FE using CBUSH element, do I need to two different Bush elements? One bush connecting Ti plate to Al plate & another one from Al to Steel plate? This is in spite of same fastener/rivet used to join all 3 plates together.

2. If the answer to the above question is yes, then I assuming that each Bush element will have its own shear spring constants definition as calculated using an appropriate fastener flexibility equation?

3. If the answer to (1) is NO, then how does one account for different materials & thicknesses in calculating flexibility.

### RE: Fastener Flexibility Application for this Scenario

you've all three plates modelled ? (say at mid-thickness)

then 2 CBUSH required.

equal stiffness (Huth for the joint) or two different stiffness (Huth for 1/2 AL + Steel, and 1/2 AL + Ti) … shouldn't make a significant difference

you can always hand calc the bolt shears later

### RE: Fastener Flexibility Application for this Scenario

I think you can use an equivalent section changing one material into one of the others using the ratio of elastic modulus ratio Of one material To the other, similar to calculating bending on a compound section.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

### RE: Fastener Flexibility Application for this Scenario

(OP)
Rb1957 & desertfox, thanks for your replies.

RB, yes all 3 plates will be modeled @ Midsurface. Actually, the thought of dividing the middle plate (Al) in to half for top & bottom never crossed my mind. Very interesting...

### RE: Fastener Flexibility Application for this Scenario

you might fuss over the proportioning between the plates … hand calc the relative stiffness of the steel and Ti plates, then proportion the Al plate similarly (if steel is taking 60% of the load, then give it 60% of the Al plate).

### RE: Fastener Flexibility Application for this Scenario

http://gbreco.pl/images/Pdf/compositebars.pdf

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

### RE: Fastener Flexibility Application for this Scenario

Nope, you need more than two CBUSH elements, because those will not enforce continuity of the fastener thru the joint. Google “Ruttman fastener modelling”

### RE: Fastener Flexibility Application for this Scenario

Is the rivet solid steel ?
Or, a structural blind "pop" rivet etc ?

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